Maxim DS87C530 Clock User Manual

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DS87C530/DS83C530 EPROM/ROM Microcontrollers with Real-Time Clock

28 of 47

TIMED-ACCESS PROTECTION

It is useful to protect certain SFR bits from an accidental write operation. The Timed-Access procedure

stops an errant CPU from accidentally changing these bits. It requires that the following instructions

precede a write of a protected bit.

MOV 0C7h, #0AAh

MOV 0C7h, #55h

Writing an AAh and then a 55h to the Timed-Access register (location C7h) opens a three-cycle window

for write access. The window allows software to modify a protected bit(s). If these instructions do not

immediately precede the write operation, then the write will not take effect. The protected bits are:

EXIF.0 BGS Bandgap Select

WDCON.6 POR Power-On Reset flag

WDCON.1 EWT Enable Watchdog Reset

WDCON.0 RWT Restart Watchdog

WDCON.3 WDIF Watchdog Interrupt Flag

ROMSIZE.2 RMS2 ROM Size Select 2

ROMSIZE.1 RMS1 ROM Size Select 1

ROMSIZE.0 RMS0 ROM Size Select 0

TRIM.7–0 — All RTC Trim Functions

RTCC.2 RTCWE RTC Write Enable

RTCC.0 RTCE RTC Oscillator Enable

EPROM PROGRAMMING

The DS87C530 follows standards for a 16kB EPROM version in the 8051 family. It is available in a UV

erasable, ceramic windowed package and in plastic packages for one-time user-programmable versions.

The part has unique signature information so programmers can support its specific EPROM options.

PROGRAMMING PROCEDURE

The DS87C530 should run from a clock speed between 4MHz and 6MHz when programmed. The

programming fixture should apply address information for each byte to the address lines and the data

value to the data lines. The control signals must be manipulated as shown in Table 9. The diagram in

Figure 5 shows the expected electrical connection for programming. Note that the programmer must

apply addresses in demultiplexed fashion to Ports 1 and 2 with data on Port 0. Waveforms and timing are

provided in the Electrical Specifications section. Program the DS87C530 as follows:

1) Apply the address value,

2) Apply the data value,

3) Select the programming option from Table 9 using the control signals,

4) Increase the voltage on V

from 5V to 12.75V if writing to the EPROM,

5) Pulse the PROG signal five times for EPROM array and 25 times for encryption table, lock bits, and other

EPROM bits,

6) Repeat as many times as necessary.

WWW.100Y.COM.TW WWW.100Y.COM.TW WWW.100Y.COM.TW

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Maxim DS87C530 Clock User Manual